The immune system may exhibit both specific and nonspecific immunity. Nonspecific immunity encompasses various cells and mechanisms such as phagocytosis (the engulfing of foreign particles or antigens) by macrophages or granulocytes, and natural killer (NK) cell activity, among others. Nonspecific immunity relies on mechanisms less evolutionarily advanced and does not display the acquired nature of specificity and memory, which are exemplary hallmarks of a specific immune response. The key differences between specific and nonspecific immunity are based upon B and T cell specificity. These cells predominantly acquire their responsiveness after activation with a specific antigen and have mechanisms to display memory in the event of future exposure to that specific antigen. As a result, vaccination (involving specificity and memory) is an effective protocol to protect against harmful pathogens.
Generally, B and T lymphocytes, which display specific receptors on their cell surface for a given antigen, produce specific immunity. The specific immune system may respond to different antigens in two ways: 1) humoral-mediated immunity, which includes B cell stimulation and production of antibodies or immunoglobulins, antigen and helper T cells (predominantly Th2), and 2) cell-mediated immunity, which generally involves T cells including cytotoxic T lymphocytes (CTLs), although other cells are also involved in the generation of a CTL response (e.g., antigen presenting cells and Th1 cells).
In the continual pursuit for safer and more effective vaccines, new technologies, including recombinant, purification and synthetic methods, have been used to improve the quality and specificity of antigens used. Purified, sub-unit and synthesized antigens demonstrate increased safety but diminished immunogenicity which has been one driver for the identification of effective adjuvant. Thus an effective adjuvant is increasingly an essential component of modern vaccines. Adjuvants are generally compounds, that when administered with an antigen (either in conjunction with, or given prior to the administration of the antigen) enhances and/or modifies the immune response to that particular antigen.
Exemplary adjuvants that have been used to enhance an immune response include aluminum compounds (all generally referred to as “Alum”), oil-in-water emulsions (complete Freund's adjuvant (CFA) is an oil-in-water emulsion containing dried, heat-killed Mycobacterium tuberculosis organisms), Saponin (isolated from the bark of Quillaja Saponoria, the adjuvant active component known as Quile A), CpG ODN (synthetic oligodeoxynucleotide containing unmethylated CpG dinucleotides), monophosphoryl lipid A (MPL) derived from the lipopolysaccharide of Salmonella minnesota Re595, Liposomes (usually made up of biodegradable materials such as phospholipids) and biodegradable polymer microspheres (made from a variety of polymers such as, polyphosphazene and polyanhydrides). The adjuvant properties of these compounds have been evaluated with each adjuvant showing advantages and disadvantages.
Polynucleotide complexes have been investigated for their various applications including acting as adjuvants. Double-stranded RNAs (dsRNAs) are very potent biologic modifiers that can exert a profound influence on cells at nanomolar concentrations. The modulating effects of dsRNA include a broad spectrum of actions at the molecular and cellular levels.
At the molecular level, dsRNAs can elicit biological effects such as interferon synthesis, induction of protein kinase, enhancement of histocompatibility antigen and inhibition of metabolism. And at the cellular level, dsRNA can elicit biological effects such as pyrogenicity, mitogenicity, macrophage activation, activation of humoral immunity, activation of cell-mediated immunity and induction of antiviral state. Immunomodulating effects of dsRNAs has been disclosed. U.S. Pat. No. 4,124,702 disclosed that double stranded polynucleotides induced interferon induction in living animal cells. U.S. Pat. No. 3,906,092 disclosed that the antibody response to an adjuvant type vaccine was augmented by incorporation in the vaccine of a polynucleotide or a complex of polynucleotides. Houston et al. established PICLC (polyinosinic acid polycytidylic acid poly-L-lysinecarboxy-methylcellulose complex) as a potent adjuvant by increasing primary antibody response without the aid of an additional adjuvant.
Polyinosinic acid-polycytidylic acid (PIC), one of most studied polynucleotide complexes, was not effective when used in monkeys and humans due to its instability in the body after administration. Thus, PIC has been modified in many ways to overcome one or another deficiency. For example, a complex of polyriboinosinic-polyribocytidylic acid with poly-L-lysine hydrobromide is about 5 to 15 times as resistant to hydrolysis by pancreatic ribonuclease as the parent PIC.
Lin et al. described that an antiviral drug comprising polyinosinic polycytidylic acid, kanamycin and calcium can be used as an adjuvant (Lin, et al., A new immunostimulatory complex (PICKCa) in experimental rabies: antiviral and adjuvant effects, Arch Virol, 131: 307-19, 1993; and Chinese Patent No. 93105862.7). The Chinese Patent No. 93105862.7 provides for the use of the general composition of Poly I:C, kanamycin and calcium (PICKCa) as an adjuvant in a vaccine for human and mammalian application. However, Lin found that that the form of PICKCa originally identified does not provide the optimal efficacy/safety profile for use as an adjuvant and also induces unacceptable adverse side effects under certain conditions.
The present invention provides novel immunogenic compositions that exhibit improved safety and efficacy profiles; and methods of use of such compositions. Subject immunogenic compositions include a polynucleotide adjuvant and an antigen.